* Enforce fixed column number at various width breakpoints.
* Bring back the filmstrip at small sizes but hide it.
* Change default maximum columns to 7.
Due to how the filmstrip size if computed I don't think there is a good way to
animate the change in size, so just ignore the toolbar, it will be hidden soon
enough.
When the reccorder joins, they have a local participant, which is not rendered,
so don't count it towards the partcipant count used for computing the tile
sizes.